Quote:
Originally Posted by select
I am sure you can just replace the battery and dont need to replace the whole key 
there are lots of youtube vids on that topic. I would try that first, as a new key from bmw certainly wont be cheap. |
You cannot replace the batteries in these keys I'm afraid. Well thats not strictly true, but you'll never get the key back together again.
If it starts the car, and its just the remote that isn't working, carry out this sequence
1.Unlock the car with the good key.
2.Get in and shut the door.
3.Switch the ignition on.
4.Switch the ignition off.
5.Remove the key.
6.Push and hold the unlock button.
7.Push the lock button 3 times.
8.Release both buttons together.
The doors will lock and unlock if initialised correctly. Repeat steps 7 and 8 immediately with the other key, they need to be initialised together.
The key needs to be used for approx 1.5 days a year to retain its charge. Hope that helps!